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First Years of Running for the LHCb Calorimeter S ystem. Sergey Filippov (Institute for Nuclear Research of RAS, Moscow) o n behalf of the LHCb collaboration. LHCb experiment. Purpose: CP violation and rare decays study. Main subsystems: - Vertex detector – Si strips

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First Years of Running for the LHCb Calorimeter S ystem

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First years of running for the lhcb calorimeter s ystem

First Years of Running for the LHCb Calorimeter System

Sergey Filippov

(Institute for Nuclear Research of RAS, Moscow)

on behalf of the LHCb collaboration

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

LHCb experiment

Purpose: CP violation and rare decays study

Main subsystems:

- Vertex detector – Si strips

- RICH1 – aerogel, C4F10

- Tracking stations – Si strips

- Warm magnet

- Inner tracker – Si

- Outer tracker – straw tubes

- RICH2 – CF4

- Calorimeter – ECAL, HCAL, preshower

- Muon stations – MWPC, GEM

- Single arm forward spectrometer: 1.9 < η < 4.9

- Impact parameter resolution 20 μm for Pt> 2 GeV/c

- dP/P from 0.4% at 5GeV/c to 0.6% at 100 GeV/c

- Invariant mass resolution: ~22 MeV/c2 for two-body B decays

JINST 3 S08005 (2008)

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

LHCbcalorimeters

  • The calorimeter system includes:

  • - Scintillator Pad Detector (SPD):

  • - 2.5X0lead converter;

  • - Preshower (PS):

  • - Electromagnetic Calorimeter (ECAL):

  • - Hadronic Calorimeter (HCAL):

  • It provides:

  • L0 trigger on high ET h, e±, γ

  • Precise measurement of e±, γ energies

  • Offline particle identification

  • Data from the calorimeters are especially important in physics analyses of:

  • radiative decays BK*γ, BSφγ, …;

    • decays with π0/η: Bπππ0, J/ψη, D0Kππ0, …;

    • decays with electrons: BK*e+e-…

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

SPD & PS design

One layer of scintillator pads each.

~6 x 8 meters, 6016 x 2 channels.

Light collection with embedded WLS fibers.

Light yield ~25 ph.el. per MIP.

Outer

Segmentation: three zones

- Inner – pad size 40x40x15 mm3

- Middle – 60x60x15 mm3

- Outer – 120x120x15 mm3

SPD

Middle

Inner

Lead

Projectivity between

SPD, PS and ECAL

PS

Inner

Outer

Middle

VFE board

Multi Anode PMT:

HAMAMATSU R760064 channels, 2x2 mm2

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

ECAL design

  • Shashlik technology:

  • 4 mm thick scintillator tiles interleaved with 2 mm thick lead plates;

  • Volume ratio Pb:Sc 2:4

  • Moliere radius ~ 35 mm;

  • Length ~25 X0 (1.1 λi);

  • Module size 121.2 x 121.2 mm2;

  • Photodetector PMT HAMAMATSU R-7899-20.

Segmentation:

- Inner, Middle and Outer zones;

- Total of 3312 modules, 6016 cells;

Test beam data:

- Light yield: ~3000 ph.el./GeV

- Energy resolution:

ECAL resolution

Test beam data

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

HCAL design

ATLAS TileCaltechnology:

- Iron/scintillator plates parallel to

the beam direction;

- The volume ratio Fe:Sc ~ 16:3;

- Instrumented depth: 1.2 m,

6 tile rows;

- ~5.6λi – used as a trigger device;

- PMT HAMAMATSU R-7899, same as for ECAL

  • Test beam data:

  • light yield 105±10 ph.el./GeV

  • energy resolution

Segmentation:

- 2 zones;

- Inner (cells 13x13 cm2);

- Outer (26x26 cm2).

Total of 1488 cells, ~8.3x6.7 m2

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

Readout electronics

- Large fluctuation of signals → maximal integration time within 25 ns slot;

- VFE board: two integrators per r/o channel alternating each 25 ns;

- 100 Front-End Boards (FEBs):

- Combines 64 ch SPD + 64 ch PS;

SPD: 1 bit signal (yes/no, 0.5 MIP thr)

PS: 10-bit ADC 40 MHz

– Parameters for pedestal subtraction, corrections for pile-up and gains;

– Digital pipe-line to store data until L0 decision

– Trigger block: production of data for L0 trigger.

SPD/PS

ECAL/HCAL

- PMT signal clipping to eliminate atail beyond 25 ns;

- 192 Ecal + 54 HcalFEBs;

- FEB: 32 ch, same for ECAL and HCAL;

–12-bit ADC 40 MHz (80 pC full range);

– Pedestal subtraction;

– Digital pipe-line to store data until L0 decision;

– Trigger block: production of data for L0 trigger.

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

SPD & PS calibration

The calibration is performed using tracks pointing to a given cell.

  • Calibration of SPD is done via threshold scan:

  • the nominal threshold corresponds to ~0.5 MIP;

  • precision on correction factors ~3% for MIPs;

  • efficiency after calibration ~95% with 3% r.m.s.

  • Nominal sensitivity is set to ~ 300 MeV max.

  • the inter-calibration of cells is based on the position of the MIP peak;

  • precision ~5%.

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

ECAL calibration

The L0 trigger decision is based on Pt cut so the nominal sensitivity of ECAL cells is set depending on their (x,y) position: Emax(θ)=(7+10/sin(θ)) GeV.

The ECAL calibration was performed in several steps:

1. Pre-calibration before the startup of LHC. Based on PMT gain measurement with LED monitoring system; precision of ~8%. Overall cell-to-cell intercalibration precision ~13%.

Clear π0 signal was observed right after the LHC startup.

133±11

2. “Energy flow” method: for each cell the correction factor is derived from comparison of its average energy deposit per event to that in neighboring cells. Does not require high statistics (~1 M events), was performed shortly after the LHC startup. Precision of ~4-5%.

3. Fine calibration using position of the π0 peak.

4. E/p calibration with electrons.

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

ECAL calibration with π0

For each cell distribution of the invariant mass of two photons is filled for γγ pairs with centre of one of γ’s cluster at this cell. The correction factor for a cell is determined from the deviation of fitted π0 mass from the PDG value. Only a subsample of clusters with low energy deposition in PS (<10 MeV) is used at this step. The procedure is iterative, 5-6 iterations. To calibrate all cells, ~100M events is needed.

Performed every month, that corresponds to ~200 pb-1 of data. Precision ~1-2%.

π0 decays with converted or non-converted photonsare used to find the absolute normalization scale (“β-factor”) for PS.The EM shower energy is calculated off-line as

Both α and β being dependent on the shower position and origin (e- or γ).

The correction is determined in ECAL + PS calibration by minimizing the π0 width.

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

ECAL calibration: E/p

Another method to monitor or correct the ECAL cell calibration is through electron E/p.

Electrons are identified by estimation of the momentum of the extrapolated tracks and energy of the matching clusters.

Used to monitor ageing with applying aging trend corrections every 40 pb-1.

Useful when statistics of π0is low for mass distribution method.

E/p for electrons in ECAL

E/p for hadrons in ECAL

2011 data

HV corrections

Annealing

after one month

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

HCAL calibration

  • Absolute calibration is done with radioactive sources:

  • two 10 mCi137Cs sources (one per each detector half) driven by hydraulic system (the same as in ATLAS TileCal)

  • a source propagates consecutively through 26 modules passing each scintillator tile. PMT anode currents are measured every 5 ms with dedicated integrators installed at the back of each phototube;

  • the response of each individual tile can be determined from analysis of currents. The average current of all the tiles of a cell is proportional to the cell’s sensitivity to hadrons;

  • the absolute scale was determined at beam tests before the LHC startup, and then verified with data;

  • precision is 3-4%r.m.s.;

  • calibration is performed on the regular basis (every 1÷3 months) during technical stops.

LED monitoring system is used to control HCAL response during data taking.

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

Particle identification

  • Electron ID. Combined likelihood fully based on real data distributions. Clean reference samples are available in data:

  • pure electron/positron sample: photon conversion γe+e-;

  • pure hadron sample: decay D0Kπ

___ electrons in ECAL

___ hadrons in ECAL

EPS(MeV)

E/p

Performance on data: ~4% misidentification rate at 90% efficiency

  • Photon ID. Based on the following observables:

  • energy deposition in PS;

  • track matching χ2 (there should be no track pointing to the Calo cluster)

  • clusters with and without SPD hits in front are treated separately.

Track – ECAL cluster matching

Photon/merged π0 separation.At high pT (>3 GeV/c) ECAL energy depositions of both γ’s from π0 decay merge into a single cluster. The separation is based on cluster shape different for single and merged photons.

Mass resolution for resolved π0– 8 MeV/c2, merged – 20 MeV/c2.

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

LHCb Detector Operation

2012

2011

2010

  • LHCb is running at a lower luminosity than ATLAS and CMS using luminosity leveling technique.

TDR, 14TeV: L=2.x10³² cm⁻² s⁻¹ with average number of interactions per event μ = 0.4

2012, 8 TeV: L=4.x10³² cm⁻² s⁻¹ with μ<=1.8

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

Aging of ECAL

Two sources of degradation:

- radiation demage of scintillator tiles and WLS fibers (~0.25 Mrad /year);

- PMT sensitivity loss.

0 mass variation as a function of time (luminosity) observed:

  • The effect is cured by calibrating of ECAL:

  • - changing of PMT HV;

  • - fine calibration of each ECAL cell using 0 and adjusting its mass on a short period of data taking;

  • - on top of fine-calibrated data trending coefficients are applied:

  • If 0 statistic not high enough to follow closely the changes

  • make use of photon conversion and look at E/p

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

Aging of HCAL

0 1 2 3 4 5

HCAL tile row

Light yield degradation in the HCAL centre

HCAL PMTs anode currents are 5 times more the for ECAL.

Integrated anode currents are up to 100C.

Gain reduction vs. integrated anode current was

studied in the lab.

  • Light yield degradation can be corrected by

  • modifying PMT gain (HV)

  • calibration with Cs source runs + LED

Lost of sensitivity for ECAL/HCAL PMTs

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

Physics performance: Radiative decays

Measurement of the ratio of branching fractions B(B0→K∗0γ )/B(B0s→φγ)

Proceed through electromagnetic transitions b->sγ. Sensitive to extensions of SM.

Invariant-mass distributions of the (a) B0→ K∗0γ and (b) B0 →K∗0γ decay candidates.

Nucl. Phys. B 867 (2013) 1-18

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

Physics performance: B0→J/ψω

First evidence of the B0→J/ψωdecay (1.0 fb−1@ √s = 7 TeV):

Invariant mass distribution for selected B0→J/ψωcandidates.

Nucl. Phys. B 867 (2013) 547-566

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

Physics performance: B0s→J/ψη(‘)

The ratio of the branching fractions of B0s→J/ψηand B0s →J/ψη’ decays is measured to be

Invariant mass distributions for selected B0s→J/ψη(‘) candidates. The thin solid orange lines show the signal B0s contributions and the orange dot-dashed lines correspond to the B0 contributions.

Nucl. Phys. B 867 (2013) 547-566

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

LHCb calorimeter upgrade

In 2015-2017, LHCb is expected to take 5-7 fb-1 of data @13 TeV. There is strong physics case to continue the flavor physics programme. This requires running at higher luminosities: (1-2)·1033 @√s = 14 TeVafter 2018.

With the present trigger organization, 1 MHz L0 limit: for all the hadronic final states, no gain from increasing the luminosity.

A fully software trigger is necessary to select desired final states.

For LHCb calorimeter system

  • PS and SPD shall be eliminated (they mainly contribute to L0 trigger)

  • DAQ @ 40MHz

    • Change in the readout electronics

  • Lower PMT gain

    • Higher luminosity

    • Ageing

  • Possibly replacement of few ECAL modules in hottest areas.

LHCb Upgrade LoI: CERN-LHCC-2011-001

LHCb Upgrade Framework TDR: CERN-LHCC-2012-007

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

Conclusions

  • During the data taking in 2010 – 2012 LHCb collected ~3.2 fb-1 of physics data;

  • The calorimeter system provided photon and electron reconstruction and input information for L0 decision perfectly well;

  • Aging of PMT, scintillators is within expectations. Under control thanks to frequent calibration procedures.

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

Thank you!

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

BACK UP

INSTR14 S.Filippov


First years of running for the lhcb calorimeter s ystem

LHCb Trigger Organization

  • Hardware Level-0 trigger

    • SPD multiplicity  CALORIMETRY

    • search for a highest ET object:

      • ET (e±/γ) > 2.7 GeV;  CALORIMETRY

      • ET (hadron) > 3.6 GeV;  CALORIMETRY

      • pT (μ) > 1.4 GeV/c;

  • up to 1 MHz output.

  • Software High Level Trigger (HLT):

    • ~30000 processes in parallel on ~1500 farm nodes.

  • Storage rate: 5 kHz.

  • Efficiency (L0+HLT):

    • ~90 % for di-muon channels;

    • ~30 % for multi-body hadronic final states – limitation from hadron trigger.

  • INSTR14 S.Filippov


    Lhcb upgrade electronics architecture

    LHCb upgrade: electronics architecture

    Current: latency-buffer in FE, and zero-suppress after L0 trigger

    Upgrade: zero-suppress in FE, no trigger decision to FE, LLT in back-end.

    Yu. Guz CHEF 2013 LHCb Calorimeter Upgrade


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